The present invention generally relates to electron beam tomography (EBT) scanners used for diagnostic imaging. In particular, the present invention relates to electron source assemblies used to create an electron beam in an EBT scanner.
Diagnostic imaging systems encompass a variety of imaging modalities, such as x-ray systems, computerized tomography (CT) systems, ultrasound systems, electron beam tomography (EBT) systems, magnetic resonance (MR) systems, and the like. Diagnostic imaging systems generate images of an object, such as a patient, through exposure to an energy source, such as x-rays passing through the patient, for example. The generated images may be used for many purposes. For instance, internal defects in an object may be detected. Additionally, changes in internal structure or alignment may be determined. Fluid flow within an object may also be represented. Furthermore, the image may show the presence or absence of items in an object. The information gained from diagnostic imaging has applications in many fields, including medicine and manufacturing.
EBT systems utilize a high energy beam of electrons to strike a target and produce x-rays for irradiating an object to be imaged. The point where the electrons strike the target is called the “beam spot”. The electron beam may be “tuned” and/or corrected to minimize error and more accurately produce a beam spot.
As described in U.S. Pat. Nos. 5,719,914 and 6,208,711, which are incorporated herein by reference in their entirety, an electron beam is produced by an electron source at the upstream end of a vacuum housing chamber. A large negative potential (e.g., −140 kV) on the cathode of the electron source accelerates the electron beam downstream along an electron beam axis. Further downstream, a beam optical system that includes magnetic focusing, quadrupole, and deflection coils focuses and deflects the beam to scan along an x-ray producing target.
Under normal use, the cathode has a lifetime of approximately 18 months and is the most likely part within an electron source to fail. Unfortunately, the cathode may also be destroyed by accidents, over-voltage conditions, or loss of vacuum, for example. Upon failure, the electron source assembly must be removed and returned to a factory facility for refurbishment and/or repair. Previous electron sources have been constructed such that the electron source housing must be cut open, such as at one or more ceramic-to-metal seals. The cathode is replaced within the assembly and then aligned with regard to the electron beam axis. After the cathode is aligned, the electron source housing ceramic-to-metal seals are replaced. Therefore, replacing the cathode has required time consuming and expensive reassembly and realignment.
Additionally, high voltage connections in previous electron sources have utilized an oil tank, which contains the high voltage receptacle. The removal and addition of the oil added further complexity and time to the repair and refurbishment process.
Thus, a need exists for a method and apparatus for providing an electron source which is oil-free and can be easily disassembled and reassembled, with a cathode which is easy to replace and align that addresses the problems noted above and previously experienced.